Chemical bond Pages 66–71 of the book

Ionic bond Metals tend to lose electrons and become cations (with positive charge). Non metals tend to gain electrons and become anions (with negative charge). Therefore, when metals and non metals are together, metals can give electrons to non metals (metals will become positively charged and non metals will become negatively charged). Positive charges (metals) and negative charges (non metals) are attracted to each other by electrostatic forces. That´s the ionic bond.

Ionic bond

In ionic bond In ionic bonds a crystal is formed. The chemical formula of a crystal tells us the proportion of atoms in the crystal. For example, in LiCl there is one atom of Cl for each atom of Li. In CaF2 there are two atoms of F for each atom of Ca.

Ionic bond

Covalent bond Non metals tend to gain electrons. When two non metals are together, they both can gain electrons by sharing them. In the covalent bond atoms share pairs of electrons.

Covalent bond: the sharing of electrons is shown in Lewis dot diagram

Covalent compounds can form molecules or crystals

Covalent bond We have already studied crystals. In molecules we have a fixed and usually small number of atoms (although there are huge molecules, the macromolecules). The formula of the methane is CH4 and each molecule of CH4 has four atoms of H and one atom of C.

Metallic bond Metals tend to lose electrons. When a lot of atoms of a metal are together, they all lose electrons: there is a crystal formed by cations with the lost electrons moving throughout the crystal (sea of electrons).

Metallic bond

Why do metals tend to lose electrons and non metals tend to gain them? The last column in the periodic table are the noble gases: He, Ne, Ar, Kr, Xe and Rn. The way electrons are placed in these atoms is very stable so the other elements will lose or gain electrons in order to have the same distribution of electrons in the layers.

Why do metals tend to lose electrons and non metals to gain them? He (helium) has two electrons in the last layer and the other nobles gases have eight electrons in their last layer. So the other elements will tend to lose or to gain electrons in order to have eight (or two, like He, in some cases) electrons in the last layer. This is called the octet rule.